lecture 11 - Organic Lecture Series CH 310/318 M LECTURE 11...

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Organic Lecture Series 1 CH 310/318 M LECTURE 11 Textbook Assignment: Chap. 6- Reactions of Alkenes Today’s Topics: Electrophilic Electrophilic Addition Addition Rxns Rxns Notice & Announcements: Exam1: Papers pick up after class (HW 3 Posted) Organic Lecture Series 2 Reactions Reactions of Alkenes of Alkenes Chapter 6 Chapter 6
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Organic Lecture Series 3 – Addition of water is called hydration. – Acid-catalyzed hydration of an alkene is regioselective; hydrogen adds preferentially to the less substituted carbon of the double bond (to the carbon bearing the greater number of hydrogens). – HOH adds in accordance with Markovnikov’s rule. CH 3 CH=CH 2 H 2 O H 2 SO 4 3 CH-CH 2 H OH Propene 2-Propanol + 3 C=CH 2 3 H 2 O H 2 SO 4 HO 3 H 3 C-CH 2 2-Methyl-2-propanol 2-Methylpropene + Addition of H Addition of H 2 O Organic Lecture Series 4 – Step 1: Proton transfer from H O + to the alkene. – Step 2: Reaction of the carbocation (an electrophile) with water (a nucleophile) gives an oxonium oxonium ion ion. – Step 3: Proton transfer to water gives the alcohol. + + + intermediate A 2 o carbocation + H O H H O H H 3 2 3 CHCH 3 slow, rate determining : : : + + + An oxonium ion H O H H 3 3 O-H 3 3 fast : + + + O H H O H H H HOH 3 3 3 3 fast : Addition of H Addition of H 2 O
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Organic Lecture Series 5 • In electrophilic addition to alkenes, there is the possibility for rearrangement if a carbocation is involved. Rearrangement Rearrangement : A change in connectivity of the atoms in a product compared with the connectivity of the same atoms in the starting material. Carbocation Carbocation Rearrangements Rearrangements Organic Lecture Series 6 – In addition of HCl to an alkene. – In acid-catalyzed hydration of an alkene. HCl ++ 2-Chloro-3,3-dimethylbutane (the expected product; 17%) 2-Chloro-2,3-dimethylbutane (the major product; 83%) 3,3-Dimethyl- 1-butene Cl H 2 SO 4 H 2 O OH 3-Methyl-1-butene 2-Methyl-2-butanol + Carbocation Carbocation Rearrangements Rearrangements
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This note was uploaded on 10/20/2011 for the course CH 310 M taught by Professor Iverson during the Fall '09 term at University of Texas at Austin.

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lecture 11 - Organic Lecture Series CH 310/318 M LECTURE 11...

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